The present invention relates to lighting fixtures generally, and particularly relates to optical systems which control the distribution of light emitted by a fixture. The invention has application in the field of indirect lighting where, for example, widespread distributions of light may be desired for washing overhead and vertical wall surfaces; it also finds application in the field of direct lighting wherein various light distribution patterns may be desired to meet particular lighting requirements.
Different light distribution patterns can be produced from direct or indirect luminaires using combinations of reflectors and or refracting lenses. An optical system might, for example, use a shaped reflector extending over the bottom of the luminaire housing behind the lamps of the luminaire and a refracting lens covering the opening of the housing. The basic goal is to provide an optical system which provides sufficient control over the distribution of light to satisfy the lighting designer's particular lighting needs.
In discussing the problems overcome by the present invention, it is useful to discuss problems that have existed with the optical performance of indirect lighting systems and prior solutions to those problems. As discussed in prior Herst, et al. U.S. Pat. No. 4,667,275, visual comfort in an interior space using indirect lighting systems is normally enhanced if the upper wall and ceiling surfaces which reflect light back into the space are uniformly illuminated. The problem is the difficulty of providing indirect lighting systems, such as systems comprised of a plurality of individual spaced apart luminaires or spaced apart runs of luminaires, with optical systems that are effective in spreading the light away from the luminaire. Without a suitable widespread illumination pattern that washes the wall surfaces over a relatively large area, wall surfaces near the indirect luminaire will exhibit substantial variations in surface brightness, typically showing up as hot spots directly over the luminaires separated by darker areas between luminaires. The resulting brightness contrast ratios on the illuminated walls produce glare that make many visual tasks, such as operating a personal computer or remote terminal having a video display screen, more difficult and fatiguing.
To overcome the visual discomfort associated with uneven light distribution patterns on wall surfaces, indirect luminaires have been devised having optical control systems which push the light from the luminaire's light source in a more lateral direction thereby providing a more effective spread of the light on the walls. Early attempts to increase the light spread involved the use of reflectors in the luminaire housing such as disclosed in Ruud, et al. U.S. Pat. No. 4,065,667. However, such attempts were limited in their efficacy due to inherent limitations of conventional reflector designs: a diffuse reflector that diffused the reflected light evenly in all directions would provide little in the way of directional control and therefor control over the light distribution pattern; on the other hand, specular reflectors, which mirror the image of the light source, would produce undesirable shadows where there was no direct line of sight between the reflector and wall surface. Indeed, specular reflecting surfaces tend to acerbate the problem of hot spots on adjacent wall surfaces by reflecting a virtual image of the light source back onto the these surfaces.
A solution to the limitation of the reflector only optics in indirect luminaires is disclosed in the above-mentioned U.S. Pat. No. 4,667,275, wherein a light control lens is provided over the top opening of the luminaire for refracting portions of the source light of the luminaire in a more lateral direction over the top of the housing side walls. By using the refracting element to effectively bend the source light as it leaves the housing cavity, the designer is able to increase the spread of light from the cavity and overcome the sharp reflected light patterns on the ceiling.
Notwithstanding improvements in optical systems such as disclosed by the U.S. Pat. No. 4,667,275 in connection with indirect lighting systems, the lighting designer is still constrained by his or her ability to control the light coming from within the luminaire cavity. This is particularly true with the recent availability and use of high efficiency, high intensity, compact fluorescent lamps such as the General Electric Biax lamp. Conventional refracting optical systems become less effective as the lighting fixture becomes smaller and more compact because the ability of an optical system to control the light distribution diminishes as the distance between the refracting elements and the light source become smaller. Heretofore, effective control over the distribution of light was not obtainable in a luminaire using an optical element very close to the source.
The present invention overcomes the foregoing limitations on optical control systems for both direct and indirect luminaires by providing a a reflecting optical system which when placed in close proximity to the luminaire's light source enhances the designer's ability to gain control over the directivity and distribution of source light closer to the light source. This can be done to achieve the purposes of the designer, such as increasing the spread of light through the unlensed opening of a luminaire housing or increasing the amount of light directed to other optical elements within the luminaire.